The sprawling ranch in Eldorado, Texas, belonging to members of the Fundamentalist Church of Jesus Christ of Latter Day Saints was raided last month by authorities acting on tips alleging physical and sexual abuse.
Officials removed more than 460 children and teens into state custody, where they remain, CNN reported Monday.
"Mr. President, it does not require a foreign country to commit terrorist acts on American soil," the letter says. "Terrorist acts can be committed by federal, local and private entities that are operating under the guise of 'protecting the public,'" FLDS elder Willie Jessop write to President George W. Bush.
The April 3 raid on the compound was an "intrusive invasion" by "a heavily armed militant force," the letter dated May 10 said.
"We are talking about homes being broken into without search warrants, unarmed fathers being forced to the ground with M16 rifles pointed at their heads, screaming children being torn from the arms of their grief-stricken mothers -- all upon American soil and within your own home state of Texas," the letter said.